Many analyte measurement systems, such as self-monitoring blood glucose (SMBG) systems, clinical blood glucose monitoring systems and laboratory blood glucose monitoring systems, are based upon amperometric, coulometric, potentiometric, voltammetric or other electrical measurement of an electro-active species produced by a reaction with an analyte such as glucose or the measurement of a direct property of the analyte matrix. A combination of these methods also can be employed for calculating an analyte concentration.
In SMBG systems, an electrochemical measurement often is performed by inserting a biosensor into a handheld meter and introducing a drop of a fluidic sample such as blood onto the biosensor that comprises a defined sample space, a dried chemical reagent and a system of electrodes. Upon detecting the sample, the meter then performs the electrical measurement, and mathematical algorithms are used to convert the results into a reliable glucose concentration.
For example, in some amperometric measurements, a test sequence is applied to a sample having an analyte of interest, where the sequence has AC potentials at different frequencies followed by a longer, fixed DC potential. A response current to the applied test sequence is monitored as the analyte is reduced or oxidized. The resulting DC current exhibits an exponential decay, as described by the Cottrell equation. As the slope of the decay decreases and approaches a constant rate of change with respect to time, the magnitude of the current can be used to quantify the analyte. The AC current is largely independent of the analyte and is more closely related to other variables such as hematocrit (Hct) and temperature.
The magnitude, rate and shape of the current decay, however, can be influenced by many variables including, but not limited to, reagent thickness, wetting of the reagent, rate of sample diffusion, Hct and temperature, as well as presence of certain interferences. These interferents, or confounding variables, can cause an increase or decrease the observed magnitude of the DC current that is proportional to an analyte such as glucose, thereby causing a deviation from the “true” glucose concentration. Efforts to combine the AC and DC current response information to generate a “true” glucose value either are extremely complex or have been largely unsatisfactory.
Current methods and systems provide some advantages with respect to convenience; however, there remains a need for alternative methods of electrochemically measuring an analyte in a fluidic sample even in the presence of confounding variables.